High-speed silent air turbine



July 6, 1965 A. L. 1.. BRUNEL ETAL 3,193,251

HIGH-SPEED SILENT AIR TURBINE Filed July 19, 1962 United States Patent3,193,251 HEGH-SJEED SILENT AlR TURBINE Andre Lucien Laurent Erunel, 182Rue de Rivoli, and Robert Maurice lviercier, 172 Blvd. du Montparnasse,both of Paris, France Filed July 19, 1962, Ser. No. 211,046 Claimspriority, application France, July 22, 1961, 568,875 Patent 1,303,056 1Claim. (Cl. 253-56) Turbines which operate more particularly withcompressed air as a driving fluid form very high speed engincs, the bulkand Weight of which are very reduced, while they are particularlysuitable for incorporation with hand tools and are used very frequentlyby dentists and for the execution of highly accurate mechanisms.

Generally speaking, such turbines include a one stage rotor subjected tothe direct impulse of a jet of compressed air.

Now, in such apparatus, the imperfect expansion of the air and the verysimple shape of the blades produce disturbing noises during operation,which are extremely objectionable for the user, while he is executing alengthy work and chiefly when such a work requires modifications in thespeed of the turbine.

We have found after a series of experiments made on the air turbinesused for dental surgery that turbines of which the normal speed is equalto 320,000 rpm. require about litres of air per minute, which leads tothe production of supersonic waves of which the fundamental frequency isequal to 40,000 cycles, while the supersonic level is equal to 75 to 90decibels at a distance of centimeters. In addition thereto, there isproduced an audible spectrum characterized by a fundamental frequency of5,000 cycles with an acoustic level of 80 to 95 decibels at a distanceof 40 centimeters.

The unvarying ratio between the fundamental acoustic frequency and thefundamental supersonic frequency throughout the range of rotary speedsof the turbine, has led us to suppose that the acoustic vibrationsproduced were constituted, in the case considered, by lower harmonics ofthe supersonsic vibrations.

On the other hand, the comparison of the supersonic frequencies with thevalues of the rotary speeds of the turbine and the number of blades ofthe turbine rotor has shown that the turbine behaved as an actual hootergenerating an acoustic vibration at the passage of each blade in frontof the nozzle projecting the jet of compressed air.

Our invention cuts out the disturbance to which the user is subjectedand which is ascribable to the vibrations produced, by the production ofvibrations of the same amplitude and same frequency but shifted by onehalfperiod.

According to our invention as applied to the case of a turbine providedwith a driving nozzle, the production of vibrations in phase oppositionwith the objectionable vibrations, is obtained by means of a secondnozzle which is exactly of the same type and size as the first nozzle,but operates the rotor at a point shifted peripherally by about one halfblade pitch.

Our invention will be readily understood from the reading of thefollowing description, reference being made to the accompanying drawingsillustrating by way of example and by no means in a limiting sensevarious embodiments of an apparatus incorporating our invention. In saiddrawings:

FIG. 1 is a front elevational view of a rotor fed by two nozzles whichare shown in section together with the diagram of the acoustic wavesproduce-d.

FIG. 2 shows a rotor having an odd number of blades and fed by twonozzles.

FIG. 3 is a front elevational view of a turbine including two rotorsseparated by a partition disc and fed by a single common nozzle which isshown in section.

FIG. 3a is a sectional view taken along the line 3a3a on FIG. 3.

FIG. 4 illustrates a turbine subjected to the action of two nozzles andthe rotor of which is enclosed inside a stationary stator.

Turning to FIG. 1, it is apparent that the rotor 1 in cluding eightblades and revolving with the spindle 2, is subjected to the act-ion oftwo jets of compressed air 3 and 3 fed by two identical nozzles 4 and 4'assuming the same slope, the same cross-section and fed by the samesupply. The rotation of the rotor across the openings of said nozzlesproduces upon passage of the blades in front of said openings, ashutting off action which generates acoustic vibrations as would be thecase for a hooter. it will be remarked that the chief point of ourinvention resides in the shifting, by one half-pitch of a blade of theangular positions of the nozzles 4 and i with reference to thecorresponding blades of the rotor. This results in that the sinusoidsillustrating the acoustic vibrations pro duced by the air passing out ofthe nozzles 4 and 4', assume the shape of the curves A and A which, byreason of the unvarying relative position between the blades withreference to the nozzles, are constantly in phase opposition so that thesum of their ordinates is constantly equal to zero, which corresponds tothe desired silence to be obtained.

.FIG. 2 illustrates a rotor 5 including an odd number of bladessubjected to the action of two nozzles 6 and 6. This novel arrangementleads to a more easy execution since the angular shifting between thetwo jets formed by the nozzles by an odd number of half blade pitches isobtained with two nozzles 6 and 6' extending in accurate parallelism,which allows executing them through the simple boring of two parallelchannels in the body of the machine.

FIGS. 3 and 3a illustrate a rotor including two elementary rotors 7 andof equal diameters, carrying a same number of blades and separated by apartition 7' constituted by a disc, while the blades of the two rotorsare angularly shifted with reference to each other by one-half bladepitch. The feed with compressed air is ensured by a single fiat nozzle 9feeding simultaneously equal outputs of compressed air onto the bladesof the two wheels '7 and 8. The shifting by one-half blade pitch betweenthe two bladings produces a shitting by one-half period between thevibrations produced by each of the associated rotors 7 and S and ensuresthe desired silence.

FIG. 4 illustrates the application of our invention to a rotor of aknown type, which is supplied together with a metal casing forming thestator. The rotor it is thus contained inside a cylindrical casing 11including two covers.

According to our invention, this rotor is fed by two nozzles 12 and 13,the angular spacing of which is equal to an odd number of half bladepitches. The air, after transferring its energy to the rotor, escapesthrough the ports 14 and 15 formed in the casing 11. By reason of theperiodical shutting oil of the ports 14 and 15 by the blades, theexhaust of air produces a hooter ellect similar to that produced by thenozzles blowing the driving compressed .air onto the rotor. To this end,also, our invention provides for an angular spacing between the ports 14and 15 equal to an odd number of half blade pitches in the mannerdisclosed for the nozzles so that acoustic and supersonic vibrationsproduced in the two ports may be in phase opposition.

In the different embodiments disclosed hereinabove by way of examples,the number of nozzles has been limited to two but, obviously, the sameresults may be obtained with any number of identical nozzles having thesame output and the same obliquity with reference to the rotor axis,provided their angular positions with reference to the rotor blades are:such that the sum of the ordinates of the curves illustrating theacoustic vibrations produced by each nozzle may be constantly equal tozero.

Lastly, it is a known fact that in certain generators of supersonicwaves forming hooters, a rotor assuming a sufiiciently high speed andprovided with a suitable number of ports or with a suitable number ofblades, generates tor the desired purposes .sounds at predeterminedfrequencies but, when rising up to normal speed conditions, producesduring a more .or less protracted period, audible sounds of a power andsonority which are highly objectionable for the neighborhood and whichhave prevented the practical use of such generators.

Now, it is possible to produce in such supersonic sound generators inaccordance with our invention, vibrations the phase of which is opposedto that for the production of which these generators are designed andthis is obtained through the incorporation of arrangements of the typedescribed hereinabove, such as auxiliary ports, nozzles or nose-pieces,the output, obliquity and size of which are identical with those of thecorresponding parts of the prior generators while their angular positionis shifted by an odd number of half blade pitches with reference to saidparts.

The operation of said auxiliary parts may be cut out when desired by anouter control system and it is possible for the operator to resort totheir operation only during the periods during which the rotor has notyet reached its operative speed and is liable to produce .audible soundsdisturbing the neighborhood. The cut-ting out of the action of theauxiliary parts restores the entire efliciency of the generator asconcerns the production of the supersonic vibrations which it is desiredto produce.

Obviously, our invention is not strictly limited to the embodimentswhich have thus been described and illushated and it covers all themodifications thereof falling within the scope of the accompanyingclaim.

What we claim is:

In a small hand held turbine powered by compressed air and chieflyintended for dental surgery purposes, the combination of .at least oneseries of blades adapted to revolve at several hundred thousand-sr.p.m., two independent jet means operative to throw onto the bladesjets of compressed air under identical conditions at predeterminedpoints along the path of travel of the outer edges of the blades, saidpoints being angularly displaced along said path by an odd number ofhalf-blade pitches to thereby oppose the production of acoustic andsupersonic vibrations, and a stator surrounding the rotor and having twoexactly identical exhaust ports for the air passing off the blades, saidports being also 'angularly displaced around the rotor axis by an oddnumber of half-blade pitches.

References Cited by the Examiner UNITED STATES PATENTS 547,667 10/95Kales 253.-14O X 781,370 1/05 Scott 253-140 803,595 11/05 Hofmann253-140 981,758 1/11 Goehler 253-440 1,189,376 7/16 Miller 253.-56 XFOREIGN PATENTS 319,746 7/02 France.

328,988 11/20 Germany.

300,002 11/28 Great Britain,

KARL J. ALBRECHT, Primary Examiner.

WALTER BERLOWITZ, JOSEPH H. BRANSON, 1a.,

Examiners.

